[Baypiggies] How to store versioned objects

[Max Slimmer]

I have an application where the user creates and saves business
objects in a database. The objects are like invoices, header and
detail lines possibly some other attachments. When the object is saved
I want to create a version, and then should the user make changes I
would save these as a subsequent version such that when I retrieve the
object I normally get the latest version (along with some version id).
If the user desires he can get a specific previous version or see
history of changes including by who and when they were made.  Keep in
mind that these objects are not very large, like an invoice :-).

Do you know of any libraries that might help with this. I suppose I
could use some version control system and a mechanism to name the
object and possibly store some of the meta data in db.

Thanks,

max